An Unnatural History of Emerging Infections

Ron Barrett + George J. Armelagos

In An Unnatural History of Emerging Infections Barrett and Armelagos
explain how infectious diseases have always been intimately tied up
with the forms of human material culture and social life — hence the
"unnatural" of the title. They trace this through three epidemiological
transitions, with an approach centred on changes in three areas:
subsistence, or nutrition and methods of food production; settlement,
especially population density and mobility; and social organisation,
notably the openings to disease provided by the weakest and most
vulnerable. Theirs is an anthropological perspective, not necessarily
disagreeing with biomedical perspectives, but attempting to set them in
their human context.

There is necessarily speculation in reconstructing "The Prehistoric
Baseline" of our earliest human ancestors, but Barrett and Armelagos
suggest that, "having examined the protective role of nutrition against
human infections today, we could infer the same protective role in our
ancestors". Foraging and hunting probably brought rich, if uncertain,
diets (as well as exposure to wild animals and their pathogens); small
groups regularly changing location would have been less vulnerable to
acute disease outbreaks and environmental sources; and a generally
egalitarian distribution of resources would have made groups less
vulnerable.

Along with agriculture, the Neolithic Revolution saw the First
Epidemiological Transition, with "The Domestication of Pathogens"
and "the first major rises of acute infectious diseases in the human
species". Barrett and Armelagos explain some of the ways we can know
about the health of dead people and populations, but the bioarchaeology
is circumstantial and alternative interpretations are possible.
So they consider the evidence for decreasing nutritional diversity
and quality, permanent settlements with increasing population density,
pathogens derived from domesticated animals, and political centralisation.
They also touch here on the "far from even" exchange of pathogens between
New and Old Worlds, looking at immunological theories but suggesting
that the disproportionate effect on the New World was partly the result
of concomitant "violence, subjugation, and forced displacement".

Starting in the mid-19th century in industrialising parts of Europe,
the Second Epidemiological Transition brought a rapid decline in
mortality baselines. "Why Germ Theory Didn't Matter" describes key
medical advances (and Germ Theory) and public health improvements (and
the Sanitary Reform Movement). It then presents the McKeown Thesis,
which argues that these, though they contributed, came too late to be
responsible for population growth starting in the UK in the mid-17th
century, and instead identifies improved nutrition as the primary
determinant in the decline of infection-related mortality; criticisms
of this hypothesis are also examined.

The developing world is not following in the footsteps of the
industrialised world, however, but is experiencing "The Worst of Both
Worlds", with a rising incidence of the chronic diseases of modernity
alongside persistence of acute infectious diseases. An increasingly
important role is being played by syndemics, interactions between multiple
diseases that exacerbate the negative effects of one or more disease.
Mortality declines have largely been driven by advances in medicine and
antibiotic use; in contrast economic growth has been patchy and often
very unevenly distributed, while the demographics of many countries have
left large ageing populations living in poverty.

In "New Diseases, Raw and Cooked", Barrett and Armelagos turn to the
current Third Transition and the rise of "a single, global disease
ecology". Taking the Hong Kong SARS outbreak in 2003 as a starting
point, they touch on bushmeat and wild birds and viral chatter (when
a zoonotic pathogen can transfer from animal to human hosts but not
yet between humans), but emphasise the role of commercial poultry and
industrial meat production. And they explain how "plague, cholera,
and the 1918 influenza pandemic illustrate the complex dynamics of
virulence and transmissibility": contrasting Attenuation and Virulence
Hypotheses may apply in different circumstances.

In "Inevitable Resistance" Barrett and Armelagos survey the mechanisms
of antibiotic resistance (and its persistence) in pathogens, but again
centre human concerns, "acknowledging the importance of pathogens while
stressing their evolution in response to human activities: the ways we
feed ourselves, the ways we populate and live together, and the ways we
relate to each other for better and worse". Key topics here include
prophylactic use and patient compliance, commercial agriculture, and
the hot-housing of multi-resistant strains in vulnerable populations.
Historical "soil" and "seed" ideas have given way to an almost exclusive
focus on the latter: "the majority of medical research (public and
private) has been devoted to the molecular characteristics of pathogens
rather than the states of human hosts and their surrounding environments".

A conclusion tackles three myths: "that emerging infections are a new
phenomena", "that emerging and re-emerging infections are primarily
natural or spontaneous phenomena", and "that the disease determinants of
our past are qualitatively different from those of the present". And,
reiterating earlier conclusions, it suggests their implications for
policies and programs: "if we understand the common and long-standing
determinants of many infections and other health problems, then we can
organize our health efforts around these fewer, upstream determinants
instead of dealing with many more downstream consequences after they
have already occurred."

With just 115 pages of text, albeit in a relatively small font on large
pages, An Unnatural History of Emerging Infections is quite focused.
It is nicely written and cogently argued, and I would have enjoyed
seeing it fleshed out at greater length. Its core ideas are important
and need to be widely disseminated, to help medical professionals and
biomedical researchers look beyond the borders of their disciplines,
but also to improve popular understanding and inform social policy.